These teachings relate generally to time validation indicators, and more particularly, to the preparation and use of time validation indicators that are easily adaptable for various time intervals of expiration, and hence capable of providing digital and distinct indication of expiration of a predetermined time period.
Various indicators have been utilized in a number of different applications for indicating when a specific time period has elapsed. For example, time-temperature indicators have been used in areas such as pharmaceutical and food industries for indicating when perishable materials, i.e. materials having a measurable shelf-life, reach a predetermined expiration date and need to be discarded. Other examples of areas for which time indicators have been utilized include general inventory management, monitoring projects and activities, security badges, and a host of other time dependent events.
Currently, the majority of known time indicators provide, after activation, a visual indication of a predetermined period of time. Many of these known time indicators provide this visual indication by way of color change through the use of dye migration or dye diffusion. For example, U.S. Pat. Nos. 4,903,254, 5,822,280, and 7,139,226 employ the use of colored indicators that migrate, once activated, through opaque films to indicate the passage of time. In these systems, the final colored state of the indicator is generated in or below the opaque layer and then migrates through this layer to become visible. Alternative efforts, such as those cited U.S. Pat. Nos. 4,212,153, 4,248,597, and 4,643,122 describe similar approaches that include the migration of an acid/base or solvent within a laminated structure containing a pH indicator, such that a color change results following activation due to a subsequent change in pH. Other known time indicators provide a color change by way of chemical reactions, such as those cited in U.S. Pat. Nos. 3,018,611 and 4,812,053 which employ an oxygen reactive material that reacts with oxygen upon exposure and produces a visual color change. Furthermore, U.S. Pat. No. 5,085,802 describes an additional color change reaction suitable for providing a visual indication of a predetermined period of time. This color change reaction involves the generation of an acid/base “in-situ” through the use of enzymes in the presence of a pH indicator, thereby producing a subsequent color change with a change in pH.
A general problem that exists with approaches based on dye migration or dye diffusion, as well as chemical reactions, to provide a visual indication of a predetermined time period is the gradual nature of the color change over the time period, thereby making it difficult for the user to ascertain exactly when the designated end point is reached. A common approach in addressing the foregoing problem is by additionally incorporating the use of a control color strip or target strip adjacent to the time indicator in order to make visual comparisons as time progresses. However, the use of color or target strips add to the cost of making and employing the time indicators, as well as still having the possibility of user error in determining when the predetermined time period has elapsed. Time indicators that rely solely on the migration of dyes, solvents, reactants, etc. cannot escape the grey scale problem since it is an inherent aspect of diffusion kinetics. Another drawback includes the inability to use such time indicators for long time periods, i.e. month(s) or year(s). Therefore, there is a continued need to develop reliable, visual time indicator systems and devices which can be used for a variety of different applications and predetermined time periods.
There have been further attempts in providing a visual indication of a predetermined period of time with the migration of jelly or liquids through a wick material to indicate the lapse or elapse of time, such as those cited in U.S. Pat. Nos. 3,954,011 and 3,962,920. These technologies impregnate the wicking material with an indicator and the progress of a fluid along the wick material is visibly indicated and used to measure or determine a lapse or elapse of time. One drawback to such approaches is that they generally require a reservoir of fluid that is needed in order to visually indicate or measure a passage of time. Such a requirement increases the cost of utilizing these types of approaches, as well as limits their applicability, etc.
Given the drawbacks of the current time indicators utilized to provide a visual indicator of a predetermined period of time, there is, therefore, a need for a time validation indicator that is capable of providing a digital (step-wise) and distinct indication when a predetermined time period has elapsed. In providing a digital and distinct indication, such a time validation indicator affords a more reliable and accurate visual indication than that of the prior art. It is also desirable, therefore, to provide a time validation indicator that is easily adaptable for use in determining expiration of a wide variety of time intervals, i.e. short or longer periods of time, resulting in more applicability. Furthermore, it also desirable to provide a time validation indicator that is inexpensive and simpler to construct and to employ than that of the prior art.